Iodine is one of the essential nutrients which our bodies need in order to function properly. It’s most well-known for being an important constituent of our thyroid hormones, which regulate metabolism and, in children, normal growth and development.

It’s also very important for brain development in unborn, and young, children. Indeed, researchers from Otago have shown that correcting mild iodine deficiency in children improves their intelligence.

Iodine is also something in which most New Zealanders, not just our children, are increasingly deficient. There are a number of reasons for this, including changing diet over the last few years and changing practices in the dairy industry. In addition, the iodine content of New Zealand soils is low, meaning that our fruits, vegetables and grains have low iodine content.

To combat this deficiency, the salt used to make bread in New Zealand (excepting organic and salt-free breads, and some home-bake bread mixes) will be replaced with iodised salt from early next month. The iodisation of bread means that people will not have to increase their salt intake in order to improve their iodine intake.

The move follows a decision by the Government to delay mandatory fortification of folic acid in bread until at least May 2012. Across the Tasman, Australian bakers were required to add folate to bread from this week in a bid to cut spina bifida rates.

Food Standards Australia New Zealand has concluded that any risk from iodine fortification is very small across all groups. A fact sheet containing more information can be found here.

The Science Media Centre gathered comment from local experts on the mandatory fortification.

Professor Christine Thomson, of the Department of Human Nutrition at the University of Otago, comments:

“Researchers in the Department of Human Nutrition at University of Otago identified the re-emergence of mild iodine deficiency in New Zealand in the early 1990s, in spite of adequate iodine status reported during the 1960s-1980s. The low iodine content of our soils was the reason for the high incidence of iodine deficiency goitre prior to iodisation of salt in the early 1940s. The reduction in iodine status (as measured by urinary iodine excretion) during the last two decades throughout New Zealand is due mainly to the reduction in the use of iodophors as a cleaning agent in the dairy industry, resulting in lower iodine content of our dairy foods. In other words, much of our iodine intake during the adequate years was coming from iodine contamination of dairy products rather than iodised salt. A reduction in the use of iodised salt at the table and in cooking as a result of changes in dietary patterns has also contributed to the recent re-emergence of mild iodine deficiency. In particular, there has been an increase in the consumption of processed foods; salt used in manufactured and processed foods is not iodised in New Zealand.

“Subsequent research by us indicated that the low iodine status is being reflected in disturbances in thyroid hormone metabolism, enlarged thyroid glands (goitre) and more recently a possible impairment in cognitive function of children. This situation is likely to worsen unless measures are taken to increase our iodine status. The most vulnerable groups in the population are pregnant and lactating women, as vital foetal mental and physical development occurs during pregnancy and during early infancy. Young children are also vulnerable to iodine deficiency in terms of cognitive and physical development.

“Mandatory fortification of bread will go some way towards safeguarding the population from iodine deficiency and will increase the iodine status of most of the population to adequate levels. However, it will not be sufficient to meet the very high requirements for iodine for pregnant women, and iodine supplements are still recommended during pregnancy.

“Universal salt iodisation (ie iodisation of all salt used in processed food and table salt) is the recommended method for eliminating iodine deficiency around the world, but has not been adopted in New Zealand and Australia because of the perceived resistance from the food industry. Bread was chosen as a convenient and relatively easy first step as the salt already in bread will simply be replaced with iodised salt.

“Iodine fortification is necessary in New Zealand ultimately because of our low soil content resulting in low iodine concentrations of food. Folic acid fortification is the replacement of a nutrient removed during processing of cereals. For both there is good evidence for beneficial effects of fortification on health. Iodine fortification is not controversial probably because we already have iodised salt and so is not a new issue for the public.

“Consumption of iodine-rich foods such as fish, sushi, eggs and dairy products is still a sensible option for improving iodine status and also provides many other essential nutrients.”

“Worldwide iodine deficiency is the biggest single cause of preventable brain damage and mental retardation. In NZ evidence from the 2002 National Children’s Nutrition Survey was that NZ children had urinary iodine excretion rates consistent with mild iodine deficiency (this is best way of measuring iodine status).

“It’s an issue in NZ because the consequences might be that children do not learn and develop as well as they might do. The effects of deficiency are seen at all stages of development but the other vulnerable time would be foetal development and when being breast fed.

“The impact of iodine fortification we would hope would lead to the most vulnerable groups becoming iodine sufficient but fortification might still not be enough. I believe that the Ministry of Health is developing a proposal for a 150 microgram iodine tab (like the folic acid tab) but when I looked on their website I could not find a reference for this. However, they do have some quite good iodine notes.

“Bread was chosen after the FSANZ modelling research which showed that this was most likely to be the most consumed food. Historically NZ had a relatively high rate of iodine deficiency because our soils are poor in iodine (soil leached by glaciation or high rainfall contains little iodine) and therefore food grown in these soils contains very little iodine. We have had iodised table salt in NZ for almost 100 years now as a public health measure to prevent iodine deficiency. However salt used in manufactured food had to be just ordinary salt. The new measure is that salt used in breadmaking now will contain iodised salt, i.e. iodine fortification. Previously, over perhaps the last 50 years or so, use of iodophors as sanitisers in the dairy industry gave us all a little extra iodine from the residues in dairy products but these are not used very much nowadays.

“It’s really not all that different from folic acid fortification but maybe New Zealanders have had almost 100 years to get used to the idea that we need a little extra iodine because they are familiar with seeing iodised salt on the supermarket shelves. Maybe people think salt is more “natural”. It is perhaps worth mentioning that it would be a bad idea to encourage New Zealanders to have more iodised salt as table salt because salt intake is one of the biggest factors driving up our collective blood pressure and consequent strokes and heart disease. So we hope that this is a win/win situation.”

Dr Sheila Skeaff, Senior Lecturer at the Department of Human Nutrition, University of Otago, comments:

“There are low levels of iodine in New Zealand soils, and it common in New Zealand for our diets to be lacking in iodine. In the past most of our iodine came from dairy foods such as milk and cheese, and iodised salt used at the table or in cooking. But today people are adding less salt to food or are replacing iodised salt with rock or sea salt that contains virtually no iodine. Changes in the dairy industry has meant that the amount of iodine in dairy foods is much lower than it used to be. Many people are not aware that the salt used to make foods bought in the supermarket (i.e. processed foods), is not iodised. And although fish and seafoods are rich in iodine, most New Zealanders do not eat enough of these foods to get much iodine from them. At present, most children and adults, especially pregnant and lactating women, are iodine deficient. Iodine is an essential element needed for normal growth and development, particularly of the brain. Growing brains need iodine and that is why pregnant women and children need a good supply of iodine in their diets.

“A recent study has found that giving New Zealand children extra iodine helped them do better on cognitive tests than children who were iodine deficient. The mandatory fortification of bread with iodised salt should increase the iodine intakes of New Zealand children and adults so they are getting enough iodine from foods, however, pregnant and lactating women will still not obtain enough iodine in this way and should take a supplement containing 150 ug of iodine each day. People who do not eat commercial breads should ensure that they obtain additional iodine from consuming more iodine-rich foods or taking an iodine-containing supplement. The use of kelp tablets, however, is not recommended as these tablets often contain variable and very high amounts of iodine. In contrast to folic acid, which is recommended for one group of the population (i.e. pregnant women), iodine is needed for all groups of the population and the replacement of non-iodised salt with iodised salt is relatively simple for food manufacturers; this may explain why the mandatory fortification of bread with iodised salt is less controversial than mandatory folic acid fortification. Nonetheless, the lack of iodine in the New Zealand diet for almost two decades has received little attention in the media, despite the possible implications this may have on brain development, both for individuals and society. In 2008 the Copenhagen Consensus, a panel of 8 top-economists including 5 Nobel Laureates, identified the iodisation of salt as the world’s third best investment to improve the state of the planet.”

David Roberts, Programme Manager for Nutrition at the New Zealand Food Safety Authority, comments:

“Why is it an issue in New Zealand?

“· Iodine is an essential nutrient for growth and development. Iodine occurs naturally in most foods, but usually in small amounts. Because iodine can’t be made in the body we need to get it from the food we eat.
· Iodine is important for our thyroid hormones. These hormones support normal growth and development in children and help to maintain the body’s metabolic rate. As iodine is essential for brain development, it is particularly important that unborn babies (foetus), infants and young children have enough iodine.
· Recent studies have indicated that the iodine status of New Zealanders is declining to the point where the New Zealand Government has decided to replace non-iodised salt with iodised salt in most bread. This will contribute to helping to reduce the risk of iodine deficiency disorders affecting the New Zealand population. Low iodine status may be due to:

people eating more commercially prepared foods (which tend to be made with non-iodised salt)

a reduction in the use of iodine-containing sanitisers by the dairy industry. Cows’ milk and foods made from cows’ milk had higher levels of iodine when the dairy industry used disinfectants containing iodine during milk processing

less salt being used in home prepared foods because of health messages encouraging consumers to reduce their salt intake

“What are the symptoms/health implications of such deficiency?

“· Low iodine levels in our diet may lead to health issues often referred to as iodine deficiency disorders. This might include poor growth and development in infants and children, including reduced intellectual quotient (IQ), thyroid diseases, and goitre (swelling of the thyroid gland in the neck).

“Who is the most vulnerable?

“· Iodine deficiency is associated with a wide range of adverse health effects; with the most detrimental involving the developing brain, especially during foetal growth and infancy periods. Hence the iodine status of pregnant and breastfeeding women is of particular importance.

· As substantial brain and nervous system development continues into the first two to three years of life, this period is also critical with respect to iodine nutrition.

· In adults, long periods of iodine deficiency increase the risk of thyroid dysfunction, predominantly hyperthyroidism and associated serious health consequences in later life.

· Further, both adults and children are at risk of developing goitre from iodine deficiency. Thus, iodine deficiency represents a significant threat to the health and wellbeing of the New Zealand community now and in the future.

“What will the impact of fortification be?

· In the general population aged 15 years and older, the proposed fortification is predicted to reduce the prevalence of inadequate iodine intakes from 51% to less than 1% overall. In children aged 5-14 years, a large improvement in status would also be achieved. In all age groups, those who do not use iodised table salt are more likely to have inadequate intakes than those who do use iodised table salt.

· The absence of New Zealand dietary survey data for young children (< 5 years) makes estimating current and post fortification intakes difficult. However, it is apparent that the proposed fortification would increase the iodine intakes of young children.

· Although the proposed mandatory fortification will increase the iodine intakes of pregnant and lactating women by an important and useful amount, it is likely that a high proportion of these groups will still have inadequate intakes. For these women, it is recommended to regularly choose foods that are naturally important sources of iodine, such as low-fat milk and milk products, eggs and seafood. Iodised salt will provide some iodine in their diet, if used instead of non-iodised salt in cooking or at the table.

· The Ministry of Health has been working to secure a subsidised iodine-only tablet to help pregnant and breastfeeding women meet their extra iodine requirements. The Ministry of Health has indicated that a daily 150 microgram iodine-only tablet will be available later this year. Once the iodine-only tablet has been assessed and approved for supply it will be available to all pregnant and breastfeeding women as an over-the-counter pharmacy product.

“Why bread?

“· One of the reasons bread was chosen is because it is eaten widely by New Zealanders. Bread manufacturers will replace non-iodised salt with iodised salt in most bread.

· Replacing non-iodised salt with iodised salt, to most bread, is a simple and low cost way of helping to increase the iodine intake of most New Zealanders, and reduce the number of people who aren’t getting enough iodine.”

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